Initial implementation of Sahsa Clock

Pygame framebuffer clock for Le Potato (ARM Debian) with aiohttp webhook server.
Renders 12-hour clock directly to /dev/fb0 (no X11/Wayland). Supports full-screen
message overlays pushed via a browser dashboard or Bearer-token API. Includes
first-run setup wizard, session-based dashboard auth, bcrypt password storage,
per-IP rate limiting, and systemd service unit.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

state.py

@@ -0,0 +1,44 @@
+import threading
+import time
+from dataclasses import dataclass, field
+
+
+@dataclass
+class MessageState:
+    _text: str | None = field(default=None)
+    _expires_at: float | None = field(default=None)  # monotonic timestamp
+    _lock: threading.Lock = field(default_factory=threading.Lock)
+
+    def set(self, text: str, duration: float | None) -> None:
+        """Set message. duration=None means persistent (no expiry)."""
+        with self._lock:
+            self._text = text
+            self._expires_at = time.monotonic() + duration if duration else None
+
+    def clear(self) -> None:
+        with self._lock:
+            self._text = None
+            self._expires_at = None
+
+    def get(self) -> tuple[str | None, float | None]:
+        """Return (text, remaining_seconds). Both None if no active message."""
+        with self._lock:
+            if self._text is None:
+                return None, None
+            if self._expires_at is not None and time.monotonic() >= self._expires_at:
+                self._text = None
+                self._expires_at = None
+                return None, None
+            remaining: float | None = None
+            if self._expires_at is not None:
+                remaining = max(0.0, self._expires_at - time.monotonic())
+            return self._text, remaining
+
+    def to_dict(self) -> dict:
+        text, remaining = self.get()
+        return {
+            "active": text is not None,
+            "text": text,
+            "remaining_seconds": round(remaining, 1) if remaining is not None else None,
+            "persistent": text is not None and remaining is None,
+        }